In the microelectronics industry as well as in other industries involving construction of microscopic structures (e.g. micromachines, magnetoresistive heads, etc.), lithography is used to obtain patterned structures of various materials such as insulators, semiconductors and/or metals in a sequence leading to the achievement of the desired structure.
Most lithographic processes (excluding so-called direct-write techniques) typically employ some type of patterned mask through which the imaging radiation is projected onto a resist material (to be patterned) on the substrate of interest. The interface between the resist layer and the substrate often presents problems in terms of interactions (chemical and/or optical) that prevent or compromise lithographic performance. For example, in the context of mask-making, if the resist layer is applied directly over chromium-containing film which comprises chromium oxynitride and/or chromium oxide over chromium on the substrate (e.g., a glass plate), footing may occur during the lithographic process which leads to a loss of pattern accuracy.
The formation of distorted profiles of chemically amplified (a.k.a., acid-catalyzed) resist on certain substrates has been attributed to poisoning by basic surface groups or surface energetics which intercept photo or generated acid near the interface and cause “footing” with positive resist or “coving” with negative resist. See K. Dean et al., SPIE Proceed., 2438, 514 (1995).
Attempts have been made to address the footing problem by treatment or alteration of the substrate (e.g., treatment with acids or oxidation of chromium), however such methods may not be compatible with device or mask production. Such treatments also add cost to the manufacturing process. Thus, there is a need for improved resist formulations which avoid these types of adverse interaction with underlying substrates, especially in the context of patterning chromium-containing materials commonly used in mask making.